1. Field of the Invention
The present invention relates to a verification apparatus and method for figure data. For example, the present invention relates to a verification apparatus and method for figure data defined by writing data used for electron beam writing.
2. Description of the Related Art
Microlithography technique, which forwards miniaturization of semiconductor devices, is extremely important because only this process performs forming a pattern in semiconductor manufacturing processes. In recent years, with an increase in high integration and large capacity of large-scale integrated circuits (LSI), a circuit line width required for semiconductor elements is becoming narrower and narrower. In order to form desired circuit patterns on these semiconductor devices, a master pattern (also called a mask or a reticle) with high precision is required. Then, since the electron beam technique for writing or “drawing” a figure has excellent resolution essentially, it is used for manufacturing such high precision master patterns.
FIG. 17 shows a schematic diagram describing operations of a conventional variable-shaped electron beam (EB) pattern writing apparatus. In the variable-shaped electron beam pattern writing apparatus, writing is performed as follows: A first aperture plate 410 has an opening or “hole” 411 in the shape of a rectangle, for example, for shaping an electron beam 330. This shape of the rectangular opening may also be a square, a rhombus, a rhomboid, etc. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 having passed through the opening 411 410 into a desired rectangular. The electron beam 330 that left a charge particle source 430 and has passed through the opening 411 is deflected by a deflector. Then, the electron beam 330 passes through a part of the variable-shaped opening 421, and irradiates a target workpiece or “sample” 340 mounted on a stage that is continuously moving in one predetermined direction (e.g. X-axis direction). In other words, a rectangular shape capable of passing through both the opening 411 and the variable-shaped opening 421 is written in a writing region of the target workpiece 340. This method of writing or “forming” a given shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a “variable shaping” method. The electron beam pattern writing apparatus of variable shaping type is disclosed in articles.
In performing electron beam writing, first a layout of a semiconductor integrated circuit is designed, and layout data (design data) for writing the design is generated. Then, the layout data is converted to generate writing data to be input into an electron beam pattern writing apparatus. Further, the writing data is converted into data of a format to be used in the electron beam pattern writing apparatus to write a pattern.
As a method for verifying whether EB data generated by converting CAD data is in accordance with the original CAD data or not, the following is disclosed in an article which describes an electron beam exposure apparatus. An exclusive OR (XOR) operation, etc. are performed between LSI design data (CAD data) and EB data generated by converting the LSI design data. Then, it is judged based on an output of the XOR operation whether the number of figures is 0 or not. When the number of figures is not 0, it operates so as to efficiently judge whether there was any conversion error at the time of data conversion or not (for example, refer to Japanese Unexamined Patent Publication No. 2001-344302 (JP-A-2001-344302)).
When converting design data into writing data, a figure which cannot be formed by using the shape of a beam forming aperture plate is approximated to a figure in accordance with the shape of the beam forming aperture plate. For example, when a pattern writing apparatus has an aperture of a triangle or a rectangle with an angle of 45 degrees, an arbitrary-angle figure that means a triangle or a rectangle having at least one angle not being an integral multiple of 45 degrees is divided into trapezoids or rectangles with an angle being an integral multiple of 45 degrees. More specifically, the triangle or a rectangle having the diagonal line portion at the angle not being an integral multiple of 45 degrees of the arbitrary-angle figure is divided into trapezoids or rectangles with an angle being an integral multiple of 45 degrees. This dividing is herein called a slit-like dividing or a slit-like division.
FIG. 18 shows an example of the design data. CAD data 210 shown in FIG. 18 is mixedly composed of non-arbitrary-angle figures 214 and 215 that mean a triangle or a rectangle all angles of which are integral multiples of 45 degrees, a figure group 217 and an arbitrary-angle figure 216.
FIG. 19 shows an example of the writing data after the conversion. Writing data 220 shown in FIG. 19 is mixedly composed of non-arbitrary-angle figures 223, 225 and 228, a figure group 227, and a slit-like divided figure group 226 being a non-arbitrary-angle figure group made by slit-like dividing the arbitrary-angle figure. The figure 228 is smaller than each figure constituting the figure group 226.
An exclusive OR (XOR) operation is performed as data verification after the conversion. If a position, a shape, etc. of a figure in the data do not change before and after the data conversion, the number of figures should become zero as the operation result. Therefore, when no figure is output as the operation result, it can be thought that no conversion error (defect) was generated. However, in the case of actually converting data, it is necessary to perform processing such as approximating an arbitrary-angle figure by a slit-like division, and converting values depending upon a change of an address unit (AU). For this reason, an operation result in a mixed state is output. Concretely, in the operation result, an error portion of the approximated figure (arbitrary-angle figure), a conversion error portion of the address unit (AU), and a conversion error portion (defect portion) which is required to obtain are intermingled. This mixed result is usually displayed on a monitor, etc. to be visually checked by a user. However, when a large number of figures are displayed as the operation result, there is a limit in judging all the figures visually. Furthermore, there is a problem in that such checking takes a lot of time and there may be checking omission.
Accordingly, it has been tried to remove figures smaller than a certain size in order to remove allowable error portions and to reduce the number of figures. FIG. 20 shows an example of the operation result. As shown in FIG. 20, figures 244 and 246 are illustrated as discrepancy portions having displacement between the figure 214 and the displaced figure 223. A figure 228, which does not exist in the design data 210 but is generated by some sort of defect in the writing data 220, is also shown as a discrepancy portion. Moreover, an arbitrary-angle figure group 242 is shown as a discrepancy portion having displacement between the arbitrary-angle figure 216 and the slit-like divided figure group 226. For the sake of brevity, it is assumed herein that no AU error is generated in the conversion. The approximation by slit-like dividing the arbitrary-angle figure is executed so that a figure difference before and after the conversion may be within a predetermined allowable error. Therefore, if a figure at the discrepancy portion of the arbitrary-angle figure outputted as the operation result is within the allowable error, the figure can be disregarded as an error. In order to remove an error portion within the allowable error of the arbitrary-angle figure, figures of the size equal to or smaller than the allowable error are deleted. Such operation result is shown in FIG. 21. According to this method, however, it becomes difficult to find other error figures smaller than the allowable error value of the arbitrary-angle figure. For example, in the case shown in FIG. 21, though the figure 228 is an error figure intrinsically, it is impossible to detect it.